PRIMITIVE ROCKS. 173 



By n rough measurement, the centre of this formation 

 on the 53rd parallel of latitude is found to be between 700 

 and 800 geographical miles from the Rocky Mountains; 

 the Great Canadian Lake district is of equal width; and La- 

 brador on to Newfoundland and the eastern shores of Nova 

 Scotia occupy a similar space in the map. Now assuming, as 

 we have done, and as the observations of the topographical 

 surveyors of the United States entitle us to do, that the 

 height at which the gentle eastern slope of the continent 

 commences is 2,500 feet, and supposing the descent to be 

 equable, we should have an altitude above the sea in the 

 country from whence the sources of the Mississippi proper, 

 the St. Lawrence, and the Red River of Lake Winipeg 

 issue, of 1,800 feet. The actual elevation of that district 

 is between 1,400 and 1,500 feet*, and the only marked 

 hilly eminence in the district, which is named the hauteur 

 des terres, and is said to consist of drift-sand and boulders, 

 does not appear, from the descriptions we have of it, to 

 rise more than 300 feet beyond the general level. The 

 summits, therefore, of this tract of land, distinguished 

 though it be by shedding its waters into three separate 

 river systems and as many different seas, are also subordi- 

 nate to the general eastern slope of the continent. 



Before naming more particularly the transverse basins 

 which cross the intermediate belt of primitive rocks, I may 

 state that the Mackenzie, inferior indeed to the Mississippi, 

 but yet a river of the first class, running in an opposite 



* Schoolcraft estimates the height of Itasca Lake, from which the 

 Mississippi issues, at 1,490 feet above the Gulf of Mexico. Major 

 Long, who ascended the St. Peter's, a head branch of the Mississippi, 

 reckons the altitude of the short portage, which sejjarates its sources 

 from those of Red River, at 1,400 feet; and my own barometrical 

 observations and estimates place the summit of the water-route be- 

 tween Lakes Superior and Winipeg, traversed by the Expedition, at 

 1,4G0 feet above the tide level of the St. Lawrence. 



